1. Field of the Invention
The present invention relates to a device and a method for converting an aspect ratio of a video signal, and more particularly, to a device and a method for converting an aspect ratio of a video signal in which an aspect ratio of an image at an arbitrary position can be converted to an arbitrary value.
2. Discussion of the Background Art
As a society is more and more information oriented, images become more and more abundant such that even general people have frequent contact with the images, and as forms of the images become to have variety, cases when the images are edited even in homes or offices are increasing more and more. Most of the editions of images up to now are done on personal computers. In most of the cases, the image edition is based on a method in which image data are read from a video RAM, make modification of the data and using the data again.
A television receiver is not a device on which edition of images can be made as it has been designed to display images as they were. Since the television receiver has in general a fixed aspect ratio of 4:3 or 16:9, when it is desired to convert the aspect ratio of the image, the conversion up to now is limited to changing of an overall aspect ratio. This is merely a processing of images for the convenience of watch rather than an image edition.
FIG. 1 illustrates a system block diagram of a general analog type deflective wave generator.
Referring to FIG. 1, the general analog type deflective wave generator is provided with horizontal and vertical sawtooth wave generating circuits 11 and 21 for generating horizontal and vertical sawtooth waves synchronous to horizontal and vertical synchronizing signals Hsync/Vsync respectively, horizontal and vertical S-form modifying circuits 12 and 22 for modifying starting and end portions of the sawtooth waves from the horizontal and vertical sawtooth wave generating circuits 11 and 21 to S-forms respectively, and current amplifiers 13 and 23 for amplifying signals from the horizontal and vertical S-form modifying circuits 12 and 22 to a prescribed levels and providing to a CRT, respectively. The horizontal and vertical sawtooth waves are set to be scanned in one direction, for example, from left to right, or from top from down, at fixed intervals.
And, a technique in which a deflection slope or a read/write clock speed of a display is controlled for changing the aspect ratio is suggested in U.S. Pat. No. 5,537,149. However, this technique can only convert an overall aspect ratio, linearly as a display ratio for an entire screen is fixed in vertical or horizontal direction of the screen. An image may be horizontally converted at a fixed ratio for all vertical directions by the horizontal S-form modification or may be vertically converted at a fixed ratio for all horizontal directions by the vertical S-form modification.
And, a technique is suggested, in which images are stored in a line memory and a field memory and subjected to compression or expansion interpolation between adjacent two pixels ro two lines, for changing the aspect ratio. However, in this technique, a ratio of the data interpolation is fixed for the entire screen in a horizontal or vertical direction, only allowing a fixed ratio conversion for the entire screen.
In the aforementioned techniques, since the scanning in general display is made in one direction(in general from left to right and from top to bottom) at fixed intervals, horizontal scanning lines and vertical scanning lines cross at right angles. That is, as shown in FIG. 2a, a regular frame of an image before conversion of an aspect ratio(an image display ratio is 1) shows a fixed ratio between scamming times and scanning distances expressed in the following equation (1) both in horizontal and vertical directions at any point 1(x1, y1) on the screen. EQU t.sub.X11 :t.sub.x12 =d.sub.x11 d.sub.12 and t.sub.y11 :t.sub.y12 =d.sub.y11 :d.sub.y12 (1)
However, there is no techniques suggested presently yet, in which an aspect ratio of only a portion of a frame is converted for an improved image better than original image or to serve for a particular purpose intentionally. If conversion of an aspect ratio for a particular portion of an entire frame is possible, an improved image can be provided by high lighting characterized part of the image, and this technique will find wide application to various fields in image display.